Three-dimensional display



R. M. CRQOKER THREE-DIMENSIONAL DISPLAY y April 6, 1965.

2 Sheets-Sheet 1 Filed Nov. 15. 1961 wm x , H .9... OO

@Enom-O 2 Sheets-Sheet 2 Filed Nov. 13. 1961 FIG. 2

FIG. 4

' 13,177,486.V i TImEE-DIMENSNAL DISPLAYV RobertV to Hazeltine Research,- Inc., a corporation of Illinois Filed Nov. 13, 1961, Ser.` No. 151,737

Claims. `(ci. sns- 7.9)l

. Y i VGeneral This invention relates to a three-dimensional `display particularly suited to `exhibit information developed by M. Crocker, Cold Spring Harbor, N.Y., assignor 3,177,486 l kRatented Apr. 6, 1965 ICC Eachmatrix 11, 12and13 comprises a crossedcondnctor `configuration and light emitting elements at the intersections of the conductors. VReferringto FIG. y2

. where afpor-tion of a matrix is shown in detail, each matrix may specifically'comprise a rst transparent sheet having a first set of parallel conductors 21 printed -thereon and agsecond transparent sheet ZZvhaving a second set of parallel conductors, 2,3 printed thereon.

``The transparent sheets 20 rand 22 may be of glass or any other nonconductive material capable of passing light at arrelatively high eiiiciency. Conductorslzl and 23 a radar system. The invention maybe employed` to`f show the air traffic-.situation inthe vicinityof anl airport.

' Another application is in contour 'mapping theterrain over which an airplane isilying.

At the present time, air traiiiciin the vicinity of airports is visually exhibited-ontwo-dimensional displays such as` the Well-known plan position indicators. -A threedimensi-onahdisplay such as one constructedin accordance with` the present invention would provide viewers with a more realistic indication ofthe actual' traliic situmay 'be deposited on transparent sheets 20 and 22, re-

spectively, Vby conventional printed wiring techniques.

While the thickness of conductors 21 and 23 has been exaggerated-in FIG. 2 merely for purposes offillustration,

i in practice their thickness would be keptr'extremely thin.

ation around the airport. Thus, a threedimensional dis-'i play wouldwarn an airport observer about possible midair collisions in a quicker andV more efcient manner than presently used indicating devices. Inaddition, an improved display device such as a three-dimensional display would permit increasing the air traffic handling capability of an airport. l v .Y

In accordance with' the,4 present invention a three-di- `mensional display com-prisesa plurality df. two-dimensional matricesfstacked in a Vthird dimension; Each The width of the conductors would also be kept to a minimum so that when a plurality of matrices are stacked,

the conduct-ors Would not appreciably obstruct the passage of light from Within thefdisplay to the surface.

The position and direction of conductors 23 are such i that when transparent sheets 20 and 22 are mated, .conductors 21 and -23 intersect. As shown in the drawing, the second set of conductors 23 isfat right `angles to the rst set 21 thus forming a crossed conductor grid conguration when transparent sheets 20 and 22 are mated.

lEach matrix 11, 12 and 13 additionally comprises Alight emitting elements 24-27, inclusive, shown' as discs placed Lbetween transparent sheets 20 and '22 at the intersections of the conductors. Light emitting elements 24- y `72, inclusive,.may be electroluminescent phosphor scells matrix comprises a crossedconductor.confiigurationland i i l y l amount of llght which may be v1ew`ed at the surface visualindicating elements at the intersections ofthese conductors. The three-dimensional display 'additionally includes means for sequentially-energizing selected pairs of conductors of any `matrix with' timeV shared signals,

thereby energizing the `visual indicating elements located at the intersections of the aforementioned `selected pairs of conductors `and preventing energizing ,of visual indicating elements located at the intersections Vof one conductor of onepair and another conductor of another pair. y

For a 'better understanding ofthe present invention,

together with other and further,` objectsthereof, reference is had to the following description taken in connection with the accompanying drawings, and itsscope will `be pointed out in thefappended claims.`

Referring to the drawings: l A. Y

FIG. l shows a` three-dimensional display constructed in accordance with the-present` invention employedl to display target-s detected by a-height and Search radar system; l

FIG. 2 shows a detaileddrawing of a portion of ama-trix inA a three-dimensional displayk constructed in accordance with the present invention; Y j

FIG. 3 `shows a crossed conductor grid configuration,

and

lFIG. 4 shows Wave-forms :of-electrical signals which may be used to energizeithe matrices of the FIG.` 1 threedimensional display. x i i Description" and operation lof the` three-'dimensional displaywl ing employedto display targetsjdetected by a height and search radar system. Referring` to FIG. 1,'a three-dimensional display comprises=a pluralityof two-dimensional rnatrices 11, `12 and13 stacked in a third dimension. As shown in the drawing, the matrices have Vtheir two dimensions in a horizontal plane andare stacked vertically, being spaced inthe verticaldirnension by aV plurality of spacers 1449, inclusive.

` o f the display when these elements aremenergized by.

p inclusive.V YThese. ceramic discs increase the breakdownY vor any other elements capable of emitting a suliicient electrical signals. Associated with the electroluminescent phosphor -cells are high dielectric ceramic discs 28-31,

. point when electrical signals are applied acrossvthe electroluminescent phosphor cells. Again, the size of Vthe electroluminescent phosphor cells and the Vhigh 'dielectric ceramic discs is kept to a minimum so as not'toV ap- Vsuiiicient amount of light.

preciably 'obstruct the light being transmitted'through the" display. On theother hand, the electroluminescent phosphor cells must be made large enough to provide a The plurality of vertically stacked two-dimensional matrices 11, 12 and 13 maybe `representative Vof al volume in space scanned by thel height and search radar system It) and each individual matrix may be representative Vof an altitude level in this volume in space. The first set of conductors of each matrix corresponding to conductors121 `ofiFIG. 2 rnay'be representative of ordinate coordinates and the second set of conductors of each matrix Vcorresponding to conductors 23 Vof FIG. 2 may be repre'- fand 3 adjacent to conductors of matrix 13 represent vabscissa and ordinate conductors..

The three-dimensional display constructed in accordance with the present invention additionally includes means forenergizing selected conductors thereby illuminating the light emitting element located at the intersection of the selected conductors. The height and Search radar system 10 in response to signals received by its `antenna 32 develops and supplies in a conventional manner electrical signals representative of the altitude and polar coordinates of targets. The polar coordinate' signals, designated (p, 6),- are supplied-along a line 10a to a' polar-to-'Can'tesian converter 33 which develops Vplanar coordinate signals, designated (X, Y), of the targets.` The polar-to-Cartesian Yconverter 33 may be of (Y) and (Z) thus are representative of the Cartesian coordinates of targets detected by the height and Search kradar system 1t?. These signals are preferably supplied f. in binary coded form for the particular processing cirl cuitry which is to be described hereinafter. three-dimensional display as shown in FIG. 1 has only `three altitude levels and three ordinate and three abscissa Since the conductors, two binary bits are suicient to describe each coordinate of the target. For a larger display, for example one having more altitude levels and abscissa or ordinate'conductors, the'number of binary bits must be increased.

The arrangement'shown in FlG. l for energizing selected conductors of Ythe display is such that the altitude coordinate signal (Z) selects` matrices corresponding to the 4altitudes of the targets while the planar coordinate signals (X) and (Y) select pairs of ordinate and abscissa conductors within selected matrices corresponding to the planar coordinates of the targets. In particular, the

(X), (Y) and (Z) signals are supplied to a shift register 34 of conventional construction and operation which supplies these binary codedsignals in parallel to storage and timing circuits 35. Six lines are shown between the shift register 34 and the storage and timing circuits 35 to carry the three coordinate signals each having two binary bits. The storage and timing circuits 35 store the target locations and when subsequently read, furnish the same information. The function and operaiton of the storage f and timing circuits 35 will be explained in more detail hereinafter.

At this point it will be sucient to assume that the storage and timing circuits 35 supply when required binary coded signals representative of the target locations.

Three binary-to-decimal converters 36, 37 and 3S all of conventional construction and operation are connected 'to the output of the storage and timing circuits 35. 'Whenever information previously stored is derived or read by the storage and timing circuits 35, the stored shown to have two input lines corresponding to the two binary bits which describe the respective coordinate of the target. Again, for a larger display more lines would kbe connected between the storage and timing circuits 35 and the binary-to-decimal converters 36, 37 and 38.

The binary-to-decimal converters develop electrical signals at any one of their three outputs in response to the two-bit binary coded input signal. Numerals 1, 2 and 3 have been Vshown immediately above the output lines of each binary-to-decimal converter to indicate that line which carries a signal in response to a corresponding binary coded signal at its input. For example, if the Cartesian coordinates (X), (Y) and (Z) are x1, lyg and z1 the top line 1 of the (X) converter, the top line 3 of the (Y) converterand the top line 1 ofthe (Z) converter carry electrical signals. Once again, for a larger display additional output lines would be needed for the binary-to-decimal converters.

Connected to the outputs of the binary-to-decimal converters 36, 37 and 38 are a plurality of AND circuits V.3g-56, inclusive, all of conventional construction and operation. Connected to the outputs of the AND circuits 39-56, inclusive, are a plurality of high voltage circuits 59-76, inclusive. Thehigh voltage circuits 59-76, inclusive, are in turn connected to the conductors which make up the crossed conductor grid configurations of the plurality of two-dimensional matrices 11, 12 and 13. For the sake of clarity only the connections between the high input terminals.

l voltage circuits 65-70, inclusive, to the conductors of the matrix 13 have been shown. The high voltage circuits 59, 6i) and 61 Would'be connected to ordinate conductors in matrix 11 and the high voltage circuits 62, 63 and 64 would be connected to ordinate conductors in the matrix 12 in the same manner that high voltage circuits 65, 66 and 6'7 are connected to the ordinate conductors in matrix 13. The high voltage circuits 74, and 76 would be connectedto the abscissa conductors of matrix 11 and the high voltage circuits 71, 72 and 73 would be connected to the abscissa conductors of the matrix 12 in the same manner that the'high voltage circuits 63, 69 and 7i) are connected to the abscissa conductors of the matrix 13. The high voltage circuits connected to the abscissa conductors supply electrical signals of one polarity equal to half the voltage required to excite the electroluminescent phosphorV cells while the high voltage circuits connected to the ordinate conductors supply electrical signals of opposite polarity also equal to half the voltage required to excite the electroluminescent phosphor cells.

The AND circuits 39-56, inclusive, operating in a conventional manner develop potential changes in their output levels whenever input signals appear at both their Such potential changes in the output levels trigger the high voltage circuit associated with that AND circuit and thus a high voltage is supplied to the conductor connected to that high voltage circuit.

As previously mentioned, the altitude coordinate signals (Z) select the matrix corresponding to the altitude of the target. This is accomplished by the manner in which the binary-to-decimal converter 37 is connected to AND circuits 39456, inclusive. For the example given above, namely the coordinates x1, 313, Z1 only the AND circuits 45, 46, 47, 48, 49 and 50 which are connected to output line 1 of the (Z) converter are capable of triggering their associated high voltage circuits. This means that only the conductors of matrix 13 corresponding to an altitude coordinate Z1 can be energized. As previously mentioned, the particular conductors in the selected matrix 13 which are energized are selected by the planar coordinate signals (X) and (Y). The binary-to-decimal converters 36 and 38 for (X) and (Y) coordinates x1, ya respectively, supply signals to AND circuit 48, 51 and 54 and 39, 42 and 45. Thus, for coordinates x1, y3, Z1, AND circuits 45 and 48 are the only AND circuits which have input signals at both input terminals. Therefore, only high Voltage circuits 65 and 68 associated with AND circuits 45 and 48, respectively, supply high voltages to the conductors to which theyare connected. High voltage circuit 68 is connected to that abscissa coordinate conductor corresponding to an abscissa coordinate x1 in matrix 13 and high voltage circuit 65 is connected to the ordinateV coordinate conductor corresponding to an ordinate coordinate ya in matrix 13. The electro-luminscent phosphor cell located at the intersection of these two conductors in matrix 13 is thereby illuminated due to the high voltages which energize the conductors which intersect at this cell.

p The foregoing description has set forth the manner in which a single target is exhibited by a three-dimensional display constructed in accordance with the present invention. This three-dimensional display is, however, capable of exhibiting a plurality of targets even if more than one target is at the `same altitude level. Referring to FIG. 3

there is shown a crossed conductor grid configuration which may represent one altitude level. If actual targets Y 5 pulses, the target locations will 'be displayed foronly a short amount of time. This vis due to the fact that the electroluminescent phosphor cells do-not possess the property `of long persistence. The problemsof ambiguity and persistence may be overcomev by energizing the conductor` pairs sequentially with repetitive time shared signals.

Referring to FIG. 4, conductor pair 1, lof FIG. 3 may be energized by its associated high voltage circuits triggered by waveform (A) during period trtz and conductor pair 2, 3 may be energized by its associated high voltagev circuits triggered by waveform (B) during period t3-t4.

Waveform (C) has also been shown kand may be used for a third target. Each conductor pair is repetitively energized by these waveforms during one radar scan period.

` By the time the radar makes one complete scannew signals are received at the antenna 32 and in the case of a moving target new coordinates `would be illuminated.

The frequency and duration of these energizing pulses is dependentupon the limitations of the electroluminescent phosphor cells and would be further selected on' the basis of the number of targets that might be simultaneously displayed in any altitude level. The time during which the pulse trains continue is setto coincide with the rate of scan of the radar. VBy energizing the conductor pairs with repetitive time shared signals, the electroluminescent phosphor cells located at the intersections of selected conductors, representative of the locations of targets, are

illuminated while those electroluminescent phosphor cells` Y located at the intersections'rof one conductor of one pair.

and another conductor of another pair are not illuminated.l -v Y Furthermore, due to the fact that only one-half of the required excitation voltage appears on any one conductor,

lighting of unselected target locations on that conductor due to stray capacity groundreturn paths will not occur.V

The storageV and timing circuits 35- derivethe time shared signals such as the ones shown in, FIG. 4. The

construction 'and Loperation 0f thestorage and timing circuits 35 are essentially the same asthat used in digital computer techniques. vIn particular, the storage may be an ordinary memory drum or a memory matrix. The

binary coded signals'supplied in parallel from the shiftV register 35` are steered to particular storage locations by the timingcircuits and aretstored in these locations until the memory is read. The timing circuits then function to readA the storage in a sequential or otherr predetermined manner and Write thesame informationback in. The

particular information derived or read outof the particular locations within the storage appears at'the output terminals of` the-storage and timing circuits 35. From thisfpoint on the operation is the same as thatrpreviously described. The binary-to-decimal converters, the AND circuits and the high voltage circuits performl their prescribed functions for each target location as it issequentially read out ofthe storage.

j It is well-known that when light leaves a medium of low refractive index ,fand enters one of highV refractiveindex,

there is a loss duetoreection at the surface. Such a loss 'may occur when the space between the plurality of matrices 11, 12 and 13 is, occupied by air. Any light which has to go through a -substantialnumber of matrices may resultl in high loss, thus `cutting downits effect at the surface of the display. `This shortcoming may be f" overcome by replacingtheV air betweenrthe matrices with mineral oilor other transparent substances having a re-.

fractive index substantially the same as the refractive index of the transparent sheets which make up the matrices.`

While there has been described what is at present considered to be the preferred'embodiment'of this invention,

it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention and it is, therefore, aimed to'cove'r `all such changesand modifications as fall within'the true spirit and scope ofthe invention.

What-is claimed is: y l. A three-dimensional display comprising: a plurality of two-dimensional matrices stacked in a third dimension, each matrix comprising` a crossed .conductor-configuration and visual indicating elements at the intersections of said conductors; and means for sequentially` energizing selected pairs of conductors of any matrix with time shared sig-` nals, thereby energizing the visual indicating elements located at the intersections of said selected pairs of conductors and preventing energizing of visual indicating elements located at the intersections of one conductor of one pair and another conductor of another pair. i 2. A three-dimensional display comprising: a plurality of two-dirnensional matrices stacked in a third dimension, each-matrix comprisinga crossedl conductor configuration and light emitting elements at the intersections of said conductors;

and means for sequentially energizing selected pairs of conductors Vof any matrix with time shared signals, thereby illuminating the light emitting elements ,located atrthe intersections of said selectedV pairs of .Y conductors Vand preventing illumination of light emit- .ting elements located ,at the intersections of one conductor of one pair and another conductor of another pair. l

.v A three-dimensional display comprising: a plurality of two-dimensional matrices stacked in a third dimension, each matrix comprising a first trans- ;1 parent sheet having Va iirst set of parallel conductors` Aprinted thereon, a second transparent sheet having a second set of parallel conductors printed thereon which intersect said first set and light emitting eley ments at the intersections of said conductors; and meansV for 'sequentially energizing selected pairs fof conductors of any matrix'with time shared signals, thereby energizing the visual indicating elet ments located at the intersections ofsaid selected pairs of conductors and preventing energizing of t and means for sequentially energizing selected pairs` of conductors of any matrix with time shared' signals, therebyillumin'ating the light emitting elements locatedl at the intersections ofsaid selected pairs of conductors and preventing illumination of light :emit- ,v ting'elements located at the intersections of one conductor of one pair and another conductor of another pair. A three-dimensional display comprising;

,a pluralityfof two-dimensional matricesv stacked in a Vthirddimension, each matrix comprising a first transparent sheet having attirst set of parallel conductors printed thereon and a second transparent sheet having a second set of` parallel conductors printed thereon at right angles to said first set to form a crossed conductor grid configuration, and electroluminescent phosphor cells .placed betweenV said sheets at the intersections of said'conductors;

and means for sequentially energizing selected pairs of conductors of any matrix with time shared signals, f `thereby illuminating Athe electroluminescent phosphor cells located at the intersections of said selected envases 'E7 Y pairs of conductors and preventing illumination of electrolumines'centV phosphor cells located at the intersections of'one conductor of one pair and another conductor of another pair.

6. A three-dimensional display comprising:

a pluralityo two-dimensional matrices stacked in a third dimension, each matrix comprising a lirst transparent sheet having a rst set of parallel conductors printed thereon and a second transparent sheet having a second set of parallel conductors printed thereon at right angles to said iirst set to form a crossed conductor grid coniiguration, and electroluminescent phosphor cells placed between said sheets at the intersections of said conductors;

means `for selecting matrices from said plurality of matrices;

and means for sequentially energizing selected pairs of conductors of any selected matrix with time shared signals, thereby illuminating the electroluminescent phosphor cells located at the intersections ot said selected pairs of lconductors and preventing illumination Vof electroluminescent phosphor cells located at the intersections of one conductor of one pair and another conductor of another? pair.

7. A three-dimensional display for a radar system comprising:

a pluralityof vertically stacked two-dimensional matrices representative of a volume in space scanned by said radar system, each matrix representative of an altitude level in said volume in space and comprising a iirst transparent sheet having a tirst set ot parallel conductors printed thereon representative of ordinate coordinates and a second transparent sheet having a second set of parallel conductors printed thereon representative of abseissa coordinates to form a crossed conductor grid configuration, and electroluminescent phosphor cells placed between said sheets at the intersections of said conductors;

means for developing electrical signals representative of the altitude and planar coordinates of targets in said Volume in space;

means responsive to said altitude coordinate signals for selectingmatrices corresponding to the altitudes or" said targets;

and means responsive to said planar coordinate signals for sequentially energizing selected pairs of ordinate and abscissa conductors of any selected matrix with time shared signals, thereby illuminating the electroluminescent phosphor cells located at the intersections of said selected pairs of conductors and representative of the locations of said targets and preventing illumination of electroluminescent phosphor cells located at the intersections of one conductor of one pair and another conductor of another pair.

8. A three-dimensional display for a height and search radar system comprising:

nescent phosphor cells placed between said sheets at the intersections or" said conductors;

means for developing electrical signals representative of the altitude coordinates of targets in said volume in space;

means for supplying electrical signals representative of the polar coordinates of said targets;

means responsive to said polar coordinate signals for developing electrical signals representative of the planar coordinates of said targets;

storage means for storing said altitude and planar coordinate signals;

means for repetitively deriving said stored altitude and planar signals in a sequential manner for one radar scan period;

means responsive to said repetitive altitude coordinate signals for selecting matrices corresponding to the altitudes of said targets;

means responsive to said repetitive planar coordinate signals for sequentially energizing selected pairs of ordinate and abscissa conductors of any selected matrix with time shared signals, thereby illuminating the electroluminescent phosphor cells located at the intersections of said selected pairs of conductors and representative of locations of said targets and preventing illumination of electroluminescent phosphor cells located at the intersections of one conductor of one pair and another conductor of another pair.

9. A three-dimensional display for a height and Search radar system comprising:

a plurality of vertically stacked two-dimensional matrices representative of a Volume in space scanned by said radar system, each matrix representative of an altitude level in said volume in space and comprising a first transparent sheet having a rst set of parallel conductors printed thereon representative of ordinate coordinates and a second transparent sheet having a second set of parallel conductors printed thereon representative of abscissa coordinates to form a crossed conductor grid configuration, and electroluminescent phosphor cells placed between said sheets at the intersections of said conductors;

means for developing binary coded electrical signals epresentative of the altitude coordinates of targets in said volume in space;

means for supplying electrical signals representative of of the polar coordinates of said targets;

means responsive to said polar coordinate signals for developing binary coded electrical signals representative of the planar coordinates of said target;

storage means for storing said binary coded altitude and planar coordinate signals;

means for repetitively deriving said stored altitude and planar signals in a sequential manner for one radar scan period;

means for repetitively converting said derived signals to decimal signals representative of said planar and altitude coordinates;

means responsive to said repetitive decimal altitude coordinate signals for selecting matrices corresponding to the altitudes of said targets;

and means responsive to said repetitive decimal planar coordinate signals for sequentially energizing selected pairs of ordinate and abscissa conductors of any selected matrix with time shared signals, thereby illuminating the electroluminescent phosphor cells located at the intersections of said selected pairs of conductors and representative of locations of said targets and preventing illumination of electroluminescent phosphor cells located at the intersections of one conductor of one pair and another conductor of another pair.

l0. A three-dimensional display for a height and search radar system comprising:

a plurality of vertically stacked two-dimensional matrices representative of a volume in space scanned by said radar system, each matrix representative of an altitude level in said volume in space and comprising a irst transparent sheet having a iirst set of parallel conductors printed thereon representative of ordinate coordinates and a second transparent sheet having a Second set of parallel conductors printed thereon V9 representative of abscissa coordinates to form a crossed conductor grid configuration, and electroluminescent phosphor cells placed between said sheets at the intersections of said conductors;

a substance having substantially the same refractive index as the refractive index of said transparent sheets placed between said plurality of matrices;

means for developing binary coded electrical signals representative of the altitude coordinates of targets in said volume in space; y

means for supplying electrical signals representative of the polar coordinates of said targets;

means responsive to said polar coordinate signals for developing binary coded electrical signals representative of the planar coordinates of said targets;

storage means for storing said binary coded altitude and planar coordinate signals;

means for repetitively deriving said stored altitude and planar signals in a sequential manner for one radar scan period;

means for repetitively converting said derived signals to decimal signals representative of said planar and altitude coordinates; Y

means responsive to said repetitive decimal altitude coordinate signals for selecting matrices corresponding to the altitudes of said targets;

and means responsive to said repetitive decimal planar coordinate signals for sequentially energizing selected pairs of ordinate and abscissa `conductors of any selected matrix with time shared signals, thereby illuminating the electroluminescent phosphor cells located at the intersections of said selected pairs of conductors and representative of locations of said targets and preventing illumination of electroluminescent phosphor cells located at the intersections of one conductor of one pair and another conductor of another pair. Y

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Crystal Ball Plots 3-D Curves in Color, by I. R. Al-

burger, Electronic Industries and Tele-Tech, February 1957. Pages -53 relied upon.

CHESTER L. JUSTUS, Primary Examiner. 

1. A THREE-DIAMENSIONAL DISPLAY COMPRISING: A PLURALITY OF TWO-DIMENSIONAL MATRICES STACKED IN A THIRD DIMENSION, EACH MATRIX COMPRISING A CROSSED CONDUCTOR CONFIGURATION AND VISUAL INDICATING ELEMENTS AT THE INTERSECTIONS OF SAID CONDUCTORS; AND MEANS FOR SEQUENTIALLY ENERGIZING SELECTED PAIRS OF CONDUCTORS OF ANY MATRIX WITH TIME SHARED SIGNALS, THEREBY ENERGIZING THE VISUAL INDICATING ELEMENTS LOCATED AT THE INTERSECTIONS OF SAID SELECTED PAIRS OF CONDUCTORS AND PREVENTING ENERGIZING OF VISUAL INDICATING ELEMENTS LOCATED AT THE INTERSECTIONS OF ONE CONDUCTOR OF ONE PAIR AND ANOTHER CONDUCTOR OF ANOTHER PAIR. 